1. Field of the Invention
The present invention relates to a facsimile apparatus and, more particularly, to a facsimile apparatus having the ability to transmit command signals in the form of a multifrequency signal using an automatic dialing function.
2. Description of the Related Art
The so-called G3 procedure standardized according to ITU-T Recommendation T.30 is widely in use for facsimile communication. Further, there are defined such signals as NSF (Non-Standard Facilities), NSC (Non-Standard facilities Command), and NSS (Non-Standard facilities Set-up) for conducting negotiations for functions not included in the standard procedure. However, since these signals are substantiated in the format or code particular to each manufacturer, negotiations between apparatuses of different manufacturers have been unattainable.
On the other hand, there are proposed facsimile systems which are equipped to transmit and receive DTMF (dual tone multifrequency) signal, i.e., the PB (push button) signal, and to execute communication control with using DTMF signal (refer to gazettes of Japanese Patent Laid-open Nos. Sho 63-104572, Sho 63-300669, Hei 2-50560, Hei 3-260875). A telephone is used as the apparatus on the side transmitting the DTMF signal in some of the related art examples, but no disclosure of it is made in the others. Thus, there has been no reference in which investigation of the method of signal detection and the method of signal transmission is made in concrete terms, and the DTMF signal has generally been described as such that is transmitted manually. Under these circumstances, there is proposed an art to have the DTMF signal transmitted automatically (refer to the gazette of Japanese Patent Laid-open No. Hei 4-168862).
Further, a system in which dial pulses are switched to DTMF signals is disclosed in the gazette of Japanese Patent Laid-open No. Hei 4-326248. In this related art example, use of the DTMF signal for starting up a facsimile application is disclosed. However, details of the protocol control are not disclosed.
To control a facsimile application using DTMF signal, it is necessary to transmit the signal at the timing that allows the apparatus on the other end of the line to correctly receive the signal. It is also necessary to confirm that the signal is correctly received by the apparatus on the other end. Considering, for example, the automatic dialing function, an existing facsimile apparatus must be matched with the apparatus on the other end. There has therefore been a problem with the above related art facsimile systems that no concrete description exists of a design having the signal receiving function on the receiving side or matching with the existing function on the transmitting side taken into consideration to thereby achieve automatic transmission of the DTMF signals.